1. Field of the Invention
The present invention relates to a ladder for use with a trench shield to allow the user to climb down the ladder into a trench located within the walls of the trench shield. More specifically, the present invention is a ladder that is movable with the trench shield when the trench shield is pulled through a trench and can be lengthened with an extension so that the ladder is of the desired length when trench shields are stacked on top of each other for use in deep trenches. The present ladder meets applicable safety standards, and usage of this ladder can prevent injuries that often occur when using other types of ladders in this type of service.
2. Description of the Related Art
When workmen need to work in a trench in the ground, such has for example when laying cable or pipe or when doing repair work on underground lines, a trench shield is employed to prevent the sides of the trench from caving in and burying the workmen. Trench shields are made of two parallel walls that are held approximately 3 feet or more apart so that the workmen can work between the walls. The walls are approximately 8 feet tall and are strong enough to shield the workmen from a possible collapse of the trench walls. The walls are also several feet in length. The most common lengths are 8, 12, 16, 20 and 24 feet.
Currently, in order for workmen to climb down the walls of the trench shield to enter the trench, they must climb down a traditional straight ladder that has been placed into the trench between the walls of the trench shield. Use of a traditional straight ladder presents several safety problems. First, if the trench is deep, often a pair of trench shields will be employed so that one trench shield is stacked on top of the other one. Often a straight ladder is not long enough to safely use in these deep trenches.
Second, in order to use a straight ladder, safety regulations require that the ladder be tied off so that it does not tip when the workmen are on the ladder and does not fall in on top of them when they are in the trench.
As work is completed in one section of the trench, it is normally necessary to move the trench shield to another section of the trench by dragging it through the trench. When a traditional straight ladder is employed with a trench shield, the lower end of the ladder rests on the bottom of the trench. In order to safely move the trench shield along the trench, the ladder must first be untied from the trench shield and then pulled out of the trench shield. Then it is safe to pull the trench shield through the trench to its new location. After the trench shield has been moved, the straight ladder is then reinserted between the trench shield walls and is again tied off. This is a time consuming procedure and workmen will often become lazy and not take the time to perform this procedure in a safe manner. For example, they may instead push the straight ladder out the back end of the trench shield so that the trench shield can be moved without removing the ladder from the trench. If they are in the trench when they push the ladder outside of the trench shield, they often place themselves at risk because once they are beyond the walls of the trench shield, they are no longer protected from falling debris and a possible cave in of the sides of the trench. Also, once the ladder is placed outside the walls of the trench shield, workmen will often use the ladder in that unprotected location rather than take the time to reposition the ladder within the trench shield and properly tying the ladder to the trench shield. Workmen have been injured and killed by falling rocks and trench cave ins while they were in a trench but outside the protective walls of the trench shield.
The present invention addresses these problems by providing a ladder that can be extended to the desired length to permit safe access to any depth of trench shield and trench. The present invention also rests on the upper lip of the trench shield instead of the bottom of the trench and therefore can be moved with the trench shield. The present ladder fits securely over the upper lip of the trench shield and is held in place by gravity so that it is not necessary to tie the ladder to the trench shield to insure that the ladder is stable and does not fall sideways or drop off of the upper lip of the trench shield. Further, the present invention is provided with a safety platform at the top of the ladder and rails that extend over the top of the ladder to make it safe and easy for the workmen to climb into and out of the trench. Still further, the present invention is provided with stand off arms so that the workmen can fully engage the main and extension rungs of the ladder with their feet along the entire length of the ladder. The present invention is designed to fit on trench shields of varying thicknesses, easily fitting on the common trench thicknesses of approximately 4 inches and approximately 8 inches.